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6.2 Managing Variables

A Variable is like a mailbox in the post office as the content of the variable

changes every now and then, just like the mailbox. In Visual Basic 2012,

variables are areas allocated by the computer memory to hold data. In

addition, each variable must be given a name. To name a variable in Visual

Basic 2012, you have to follow a set of rules.

6.2.1 Variable Names

The following are the rules when naming the variables in Visual Basic

2012

It must be less than 255 characters

No spacing is allowed

It must not begin with a number

Period is not permitted

Some examples of valid and invalid variable names are displayed in Table

6.4

Table 6.4

Valid Name Invalid Name

My_Car My.Car

ThisYear 1NewBoy

Long_Name_Can_Be_USED He&HisFather *& Not allowed

6.2.2 Declaring Variables

In Visual Basic 2012, we need to declare a variable by assigning a name

and a relevant data type before using it. If you fail to do so, the program

may encounter an error. Usually, we declare the variables in the general

section of the code window using the Dim statement. The syntax to declare

a variable is as follows:

DimVariable Name AsData Type

Example 6.1

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles

MyBase.Load

Dim password As String

Dim yourName As String

Dim firstnum As Integer

Dim secondnum As Integer

Dim total As Integer

Dim doDate As Date

End Sub

You may also combine them in one line, separating each variable with a

comma, as follows:

Dim password As String, yourName As String, firstnum As

Integer,.............

For string declaration, there are two possible forms, one for the variable-

length string and another for the fixed-length string. For the variable-length

string, just use the same syntax as example 6.1 above. However, for the

fixed-length string, you have to use the syntax as shown below:

DimVariableNameAsString * n

where n defines the number of characters the string can hold.

Example 6.2:

Dim yourName As String * 10

yourName can hold no more than 10 Characters.

6.2.3 Assigning Values to Variables

After declaring various variables using the Dim statements, we can assign

values to those variables. The syntax of an assignment is

Variable=Expression

The variable can be a declared variable or a control property value. The

expression could be a mathematical expression, a number, a string, a

Boolean value (true or false) and etc. The following are some examples:

firstNumber=100

secondNumber=firstNumber-99

username ="John Lyan"

userpass.Text = password

Label1.Visible = True

Command1.Visible = false

Label4.Caption = textbox1.Text

ThirdNumber = Val(usernum1.Text)

total = firstNumber + secondNumber+ThirdNumber

6.3 Constants

Constants are different from variables in the sense that their values do not

change during the running of the program.

6.3.1 Declaring a Constant

The syntax to declare a constant is:

Const Constant Name As Data Type = Value

Example 6.3

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Const Pi As Single = 3.142 Const Temp As Single = 37 Const Score As Single = 100 End Sub End Class

1. Mathematical Operations

In Visual Basic 2012, we can write code to instruct the computer to perform

mathematical operations. To write code for mathematical operations, we

need to use arithmetic operators. Visual Basic 2012 arithmetic operators

are very similar to the normal arithmetic operators, only with little

variations. The plus and minus operators are the same while the

multiplication operator uses the * symbol and the division operator uses

the / symbol. The list of Visual Basic 2012 arithmetic operators is shown

in Table 7.1.

Table 7.1

Operator Mathematical Function Example

+ Addition 1+2=3

– Subtraction 10-4=6

^ Exponential 3^2=9

* Multiplication 5*6=30

/ Division 21/7=3

Mod

Modulus(returns the remainder of an integer

division)

15 Mod

4=3

\ Integer Division(discards the decimal places) 19/4=4

Example 7.1

In this program, insert two Textboxes, four labels, and a button. Click the

button and enter the code as shown below. When you run the program, it

will perform the four basic arithmetic operations and displays the results

on the four labels.

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim num1, num2, sum, difference, product, quotient As Single num1 = CSng(TextBox1.Text) num2 = CSng(TextBox2.Text) sum = num1 + num2 difference = num1 - num2 product = num1 * num2 quotient = num1 / num2 Label1.Text = CStr(sum) Label2.Text = CStr(difference) Label3.Text = CStr(product) Label4.Text = CStr(quotient) End Sub End Class

Example 7.2

The program can use Pythagoras Theorem to calculate the length of

hypotenuse c given the length of the adjacent side a and the opposite side

b. In case you have forgotten the formula for the Pythagoras Theorem, it is

written as

c^2=a^2+b^2

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim a, b, c As Single a = CSng(TextBox1.Text) b = CSng(TextBox2.Text) c = CSng((a ^ 2 + b ^ 2) ^ (1 / 2)) Label1.Text = CStr(c) End Sub End Class

Example 7.3: BMI Calculator

A lot of people are obese now and it could affect their health seriously.

Obesity has proven by the medical experts to be one of the main factors

that bring many adverse medical problems, including the cardiovascular

disease. If your BMI is more than 30, you are considered obese. You can

refer to the following range of BMI values for your weight status.

Underweight = <18.5

Normal weight = 18.5-24.9

Overweight = 25-29.9

Obesity = BMI of 30 or greater

To calculate your BMI, you can create a VB BMI calculator. The BMI

calculator can calculate the body mass index or BMI of a person based on

the body weight in kilogram and the body height in meter. BMI can be

calculated using the formula weight/( height )^2, where weight is measured

in kg and height in meter. If you only know your weight and height in lb

and feet, then you need to convert them to the metric system (you could

indeed write a VB program for the conversion).

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim height, weight, bmi As Single height = CInt(TextBox1.Text) weight = CInt(TextBox2.Text) bmi = CSng((weight) / (height ^ 2)) Label1.Text = CStr(bmi) End Sub End Class

The output is shown in the Figure 7.1. In this example, your height is

1.80m( about 5.11foot), your weight is 75 kg (about 168Ib), and your BMI

is about 23.14815. The reading suggests that you are healthy. (Note; 1

foot=0.3048, 1 lb= 0.45359237 kilogram)

Figure 7.1

From the above examples, you can see that writing code that involve

arithmetic operations is relatively easy. Here are more arithmetic projects

you can try to program:

Area of a triangle

Area of a rectangle

Area of a circle

Volume of a cylinder

Volume of a cone

Volume of a sphere

Compound interest

Future value

Mean

Variance

Sum of angles in polygons

Conversion of lb to kg

Conversion of Fahrenheit to Celsius

2. String Manipulation

8.1 String Manipulation Using + and & signs.

In Visual Basic 2012, strings can be manipulated using the & sign and the

+ sign, both perform the string concatenation which means combining two

or more smaller strings into larger strings. For example, we can join

“Visual”,”Basic” and “2012” into “Visual Basic 2012” using

“Visual”&”Basic” or “Visual “+”Basic”, as shown in the Examples below

Example 8.1(a)

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim text1, text2, text3, text4 As String text1 = "Visual" text2 = " Basic" text3 = " 2012" text4 = text1 + text2 + text3 MsgBox("text4") MsgBox(text4) End Sub End Class

The line text4=text1+ text2 + text3 can be replaced by text4=text1 & text2

&text3 and produces the same output. However, if one of the variables is

declared as numeric data type, you cannot use the + sign, you can only use

the & sign.

Example 8.1(b)

Public Class Form1 Private Sub Label1_Click(sender As Object, e As EventArgs) Handles Label1.Click Dim text1, text3 As String Dim Text2 As Integer text1 = "Visual Basic " Text2 = 2012 text3 = text1 + Text2 Label1.Text = text3 End Sub End Class

This code will produce an error because of data mismatch. However, using

& instead of + will be all right.

Public Class Form1 Private Sub Label1_Click(sender As Object, e As EventArgs) Handles Label1.Click Dim text1, text3 As String Dim Text2 As Integer text1 = "Visual Basic " Text2 = 2012 text3 = text1 & Text2 Label1.Text = text3 End Sub End Class

You can combine more than two strings to form a larger string, like the

following example:

Public Class Form1

Private Sub Button1_Click(sender As Object, e As EventArgs)

Handles Button1.Click

Dim text1, text2, text3, text4, text5, text6 As String

text1 = "Welcome"

text2 = " to"

text3 = " Visual"

text4 = " Basic"

text5 = " 2012"

text6 = text1 + text2 + text3+text4+text5

Label1.Text = text6

End Sub

End Class

Running the above program will produce the following screen shot.

Figure 8.1

8.2 String Manipulation Using VB2012 Built-in Functions

A function is similar to a normal procedure but the main purpose of the

function is to accept a certain input and return a value which is passed on

to the main program to finish the execution. There are numerous string

manipulation functions built into Visual Basic 2012 but I will only discuss

a few here and will explain the rest of them in later lessons.

8.2 (a) The Len Function

The Len function returns an integer value which is the length of a phrase

or a sentence, including the empty spaces. The syntax is Len (“Phrase”)

For example,

Len (Visual Basic) = 12

and

Len (welcome to VB tutorial) = 22

Example 8.3

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Label1.Text = CStr(Len(TextBox1.Text)) End Sub End Class

The output:

Figure 8.2

8.2(b) The Right Function

The Right function extracts the right portion of a phrase. The format for

Visual Basic 6 is

Right ("Phrase", n)

Where n is the starting position from the right of the phrase where the

portion of the phrase is going to be extracted. For example,

Right("Visual Basic", 4) = asic

However, this syntax is not applicable in VB2012. In VB2012, we need

use the following format

Microsoft.VisualBasic.Right("Phrase",n)

Example 8.4

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim text1 As String text1 = TextBox1.Text Label1.Text = Microsoft.VisualBasic.Right(text1,5) End Sub End Class

The above program returns four rightmost characters of the phrase entered

into the textbox.

The Output:

Figure 8.3

*The reason of using the full reference is because many objects have the

Right properties so using Right on its own will make it ambiguous to Visual

Basic 2012.

8.2(c)The Left Function

The Left function extracts the left portion of a phrase. The syntax is

Microsoft.VisualBasic.Left("Phrase",n)

Where n is the starting position from the left of the phase where the portion

of the phrase is going to be extracted. For example,

Microsoft.VisualBasic.Left (“Visual Basic”, 4) = Visu .

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim text1 As String text1 = TextBox1.Text Label1.Text = Microsoft.VisualBasic.Left(text1,4) End Sub End Class

3. Using If…Then…Else

In this lesson, you will learn how to write Visual Basic 2012 code that can

make decisions when it processes input from the user controls the program

flow.

9.1 Decision Making using If…Then…Else

For example, we can write a Visual Basic 2012 program that can ask the

computer to perform a certain task until a certain condition is met or a

program that will reject non-numeric data. In order to control the program

flow and to make decisions, we use the If…Then…Else control structure.

The if…Then…Else control structure employs the conditional operators

and the logical operators to make decision.

9.2 Conditional Operators

The conditional operators are powerful tools that resemble mathematical

operators. These operators allow a Visual Basic 2012 program to compare

data values and then decide what actions to take, whether to execute a

program or terminate the program and more. They are also known as

numerical comparison operators. Normally they are used to compare two

values to see whether they are equal or one value is greater or less than the

other value. The comparison will return a true or false result. These

operators are shown in Table 9.1.

Table 9.1 Conditional Operators

Operator Description

= Equal to

> Greater than

< Less than

>= Equal to or Greater than

<= Less than or Equal to

<> Not equal to

9.2 Logical Operators

Sometimes we might need to make more than one comparison before a

decision can be made. In this case, using numerical comparison operators

alone is not sufficient, we need to use the logical operators. These logical

operators are shown in Table 9.2.

Table 9.2 Logical Operators

Operator Description

And Both input sides must be true to get a true output

Or One side or other must be true

Xor One side or other must be true but not both

Not Negates true

* In making strings comparison, there are certain rules to follows: Upper

case letters are less than lowercase letters, "A" < "a" ,

"A"<"B"<"C"<"D"…….<"Z" and numbers are less than letters 21 < "A".

9.3 Using the If control structure with the Comparison Operators

To effectively control the Visual Basic 2012 program flow, we shall use

the If control structure together with the conditional operators and logical

operators. There are basically three types of If control structures,

namely If….Then statement, If….Then… Else statement

and If….Then….ElseIf statement.

9.3(a) If….Then Statement

This is the simplest control structure which instructs the computer to

perform a certain action specified by the Visual Basic 2012 expression if

the condition is true. However, when the condition is false, no action will

be performed. The syntax for the if…then.. statement is

If condition Then Visual Basic 2012 expression End If

Example 9.1

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim myNumber As Integer myNumber = CInt(TextBox1.Text) If myNumber > 100 Then Label1.Text = " You win a lucky prize" End If End Sub End Class

* When you run the program and enter a number that is greater than 100,

you will see the “You win a lucky prize” statement. On the other hand, if

the number entered is less than or equal to 100, you don’t see any display.

9.3(b) If….Then…Else Statement

Using just If….Then statement is not very useful in programming and it

does not provide choices for the users. In order to provide a choice, we can

use the If….Then…Else Statement. This control structure will ask the

computer to perform a certain action specified by the Visual Basic 2012

expression if the condition is met. And when the condition is false, an

alternative action will be executed.

The syntax for the if…then… Else statement is

If condition Then Visual Basic 2012 expression

Else Visual Basic 2012 expression

End If

Example 9.2

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim myNumber As Integer Dim age As Integer myNumber = CInt(TextBox1.Text) age = CInt(TextBox2.Text) If myNumber > 100 And age > 60 Then Label1.Text = " Congratulation! You win a lucky prize" Else Label1.Text = " Sorry, You did not win any prize" End If End Sub End Class

* This program use the logical operator And besides the conditional

operators. This means that both the conditions must be fulfilled in order for

the conditions to be true, otherwise, the second block of code will be

executed. In this example, the number entered must be more than 100 and

the age must be more than 60 in order to win a lucky prize, any one of the

above conditions not fulfilled will disqualify the user from winning a prize.

9.3(c) If….Then…ElseIf Statement

If there are more than two alternative choices, using just If….Then….Else

statement will not be enough. In order to provide more choices, we can use

the If….Then…ElseIf Statement. executed. The general format for the

if…then… Else statement is:

If condition Then Visual Basic 2012 expression ElseIf condition Then Visual Basic 2012 expression ElseIf condition Then Visual Basic 2012 expression Else Visual Basic 2012 expression End If

Example 9.4

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim Mark As Integer Dim Grade As String Mark = CInt(TextBox1.Text) If Mark >= 80 Then Grade = "A" Label1.Text = "A" ElseIf Mark >= 60 And Mark < 80 Then Grade = "B" Label1.Text = "B" ElseIf Mark >= 40 And Mark < 60 Then Grade = "C" Label1.Text = "C" Else Grade = "D" Label1.Text = "D" End If End Sub End Class

4. Using Select Case

The Select Case control structure is slightly different from the If….ElseIf

control structure .The difference is that the Select Case control structure

basically only make a decision on one expression or dimension (for

example the examination grade) while the If …ElseIf statement control

structure may evaluate only one expression, each If….ElseIf statement

may also compute entirely different dimensions. Select Case is preferred

when there exist multiple conditions as using If… Then… ElseIf

statements will become too messy.

conditions using If…Then..ElseIf statements will become too messy.

10.1 The Select Case Structure

The syntax of the Select Case control structure in Visual Basic 2012 is as

follows:

Select Case test expressionCase expression list 1 Block of one or more statements

Case expression list 2 Block of one or more Statements

Case expression list 3 . Case Else

Block of one or more Statements End Select

10.2 The usage of Select Case is shown in the following examples

Example 10.1

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click ' Examination Grades Dim grade As String grade = TextBox1.Text Select Case grade Case "A" Label1.Text = "High Distinction" Case "A-" Label1.Text = "Distinction" Case "B" Label1.Text = "Credit" Case "C" Label1.Text = "Pass" Case Else Label1.Text = "Fail" End Select

End Sub End Class

Example 10.2

In this example, you can use the keyword Is together with the comparison

operators

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim mark As Single mark = CSng(TextBox1.Text) Select Case mark Case Is >= 85 Label1.Text = "Excellence" Case Is >= 70 Label1.Text = "Good" Case Is >= 60 Label1.Text = "Above Average" Case Is >= 50 Label1.Text = "Average" Case Else Label1.Text = "Need to work harder" End Select End Sub End Class

Example 10.3

Example 10.2 can be rewritten as follows:

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 'Examination Marks Dim mark As Single mark = CSng(TextBox1.Text) Select Case mark Case 0 To 49 Label1.Text = "Need to work harder" Case 50 To 59 Label1.Text = "Average" Case 60 To 69 Label1.Text = "Above Average" Case 70 To 84 Label1.Text = "Good" Case 85 To 100 Label1.Text = "Excellence" Case Else

Label1.Text = "Wrong entry, please reenter the mark" End Select End Sub End Class

Example 10.4

Grades in high school are usually presented with a single capital letter such

as A, B, C, D or E. The grades can be computed as follow:

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 'Examination Marks Dim mark As Single mark = CSng(TextBox1.Text) Select Case mark Case 0 To 49 Label1.Text = "E" Case 50 To 59 Label1.Text = "D" Case 60 To 69 Label1.Text = "C" Case 70 To 79 Label1.Text = "B" Case 80 To 100 Label1.Text = "A" Case Else Label1.Text = "Error, please re-enter the mark" End Select End Sub End Class

The output of Example 10.4

Figure 10.1

5. Looping

Looping is required when we need to process something repetitively until

a certain condition is met. For example, we can design a program that adds

a series of numbers until the sum exceeds a certain value. We can also write

a program that prompts the user to enter data repeatedly until he or she

enters the word ‘Finish’. In Visual Basic 2012, there are three types of

Loops, they are the For…..Next loop, the Do loop. and the While…..End

while loop

11.1 Looping using the For….Next Loop

The syntax is:

For counter=startNumber to endNumber (Step increment) One or more VB statements

Next

To exit a For…..Next Loop, you can place the Exit For statement within

the loop, please refer to example 11.1 d.

Example 11.1 a

Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim counter As Integer For counter = 1 To 10 ListBox1.Items.Add(counter) Next End Sub End Class

* The program will enter number 1 to 10 into the list box.

Example 11.1b

Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim counter, sum As Integer For counter = 1 To 100 Step 10 sum += counter ListBox1.Items.Add(sum)

Next End Sub End Class

* The program will calculate the sum of the numbers as follows:

sum=1, (1+10+1), (12+20+1), (33+30+1), (64+40+1), ……

Example 11.1c

Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim counter, sum As Integer sum = 1000 For counter = 100 To 5 Step -5 sum -= counter ListBox1.Items.Add(sum) Next End Sub End Class

*Notice that increment can be negative.

The program will compute the subtraction as follow:

1000-100-95-90-……….

Example 11.1d

Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim n As Integer For n = 1 To 10 If n > 6 Then Exit For Else ListBox1.Items.Add(n) End If Next End Sub End Class

The process will stop when n is greater than 6.

11.2 The Do Loop

The Do Loop structures are

a)

Do While condition

Block of one or more statements

Loop

b)

Do


Loop While condition

c)

Do Until condition


Loop

d)

Do


Loop Until condition

* Exiting the Loop

Sometimes we need to exit a loop prematurely because of a certain

condition is fulfilled. The syntax to use is known as Exit Do. Let’s examine

the following examples

Example 11.2(a)

Do while counter

* The above example will keep on adding until counter >1000.

The above example can be rewritten as

Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim counter As Integer Do TextBox1.Text = CStr(counter) counter += 1 Loop Until counter > 1000 End Sub End Class

Example 11.2(b)

Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim sum, n As Integer ListBox1.Items.Add("n" & vbTab & "Sum") ListBox1.Items.Add("----------------------") Do n += 1 sum += n ListBox1.Items.Add(n & vbTab & sum) If n = 100 Then Exit Do End If Loop End Sub End Class

6. Functions

A function is a procedure that returns a value which is passed on to the

main procedure to finish the execution. There are two types of functions in

Visual Basic 2012, the built-in functions (or internal functions) and the

functions created by the programmers. The syntax of a function is:

Function Name (arguments)

The arguments are values that are passed on to the function.

In this lesson, we are going to learn two very basic but useful internal

functions of Visual Basic 2012 , i.e. the MsgBox( ) and InputBox ( )

functions.

12.1 MsgBox ( ) Function

The MsgBox function produces a pop-up message box and prompts the

user to click on a command button before he /she can continues. This

syntax is as follows:

yourMsg = MsgBox(Prompt, Style Value, Title)

The first argument, Prompt, will display the message in the message box.

The Style Value will determine what type of command buttons appear on

the message box, please refer to Table 12.1 for types of command button

displayed. The Title argument will display the title of the message board.

Table 12.1

Style Value Named Constant Buttons Displayed

0 vbOkOnly Ok button

1 vbOkCancel Ok and Cancel buttons

2 vbAbortRetryIgnore Abort, Retry and Ignore buttons.

3 vbYesNoCancel Yes, No and Cancel buttons

4 vbYesNo Yes and No buttons

5 vbRetryCancel Retry and Cancel buttons

We can use named constants in place of integers for the second argument

to make the programs more readable. In fact, Visual Basic 2012 will

automatically show up a list of named constants where you can select one

of them.

Example:

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click MsgBox("Click OK to Proceed", MsgBoxStyle.OkOnly, "Startup Menu") End Sub End Class

and

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim youMessage As Integer youMessage = MsgBox("click ok to proceed", CType(1, MsgBoxStyle), "Startup Menu")

End Sub End Class

are the same.

youMessage is a variable that holds values that are returned by the MsgBox

( ) function. The values are determined by the types of buttons being

clicked by the users. It has to be declared as Integer data type in the

procedure or in the general declaration section. Table 12.2 shows the

values, the corresponding named constant and buttons.

Table 12.2

Value Named Constant Button Clicked

1 vbOk Ok button

2 vbCancel> Cancel button

3 vbAbort Abort button

4 vbRetry Retry button

5 vbIgnore Ignore button

6 vbYes Yes button

7 vbNo No button

Example 12.1

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim testmsg As Integer testmsg = MsgBox("Click to test", CType(1, MsgBoxStyle), "Test message") If testmsg = 1 Then MessageBox.Show("You have clicked the OK button") Else MessageBox.Show("You have clicked the Cancel button") End If End Sub End Class

To make the message box looks more sophisticated, you can add an icon

besides the message. There are four types of icons available in VB2012 as

shown in Table 12.3

Table 12.3

Value Named Constant Icon

16 vbCritical

3 vbQuestion

48 vbExclamation

64 vbInformation

Example 12.2

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim testMsg As Integer testMsg = MsgBox("Click to Test", CType(vbYesNoCancel + vbExclamation, MsgBoxStyle), "Test Message") If testMsg = 6 Then MessageBox.Show("You have clicked the yes button") ElseIf testMsg = 7 Then MessageBox.Show("You have clicked the NO button") Else MessageBox.Show("You have clicked the Cancel button") End If End Sub

End Class

The first argument, Prompt, will display the message

Figure 12.1

12.2 The InputBox( ) Function

An InputBox( ) function will display a message box where the user can

enter a value or a message in the form of text. The syntax is,

myMessage= Microsoft.VisualBasic.InputBox(Prompt, Title, default_text,

x-position, y-position)

myMessage is a variant data type but typically it is declared as a string,

which accepts the message input by the users. The arguments are explained

as follows:

Prompt – The message displayed normally as a question asked.

Title – The title of the Input Box.

default-text – The default text that appears in the input field where the

user can use it as his or her intended input or he or she may change to the

message he wishes to enter. x-position and y-position – the position or the

coordinates of the input box.

However, in Visual Basic 2012 because InputBox is considered a

namespace. So, you need to key in the full reference to the Inputbox

namespace.

Example 12.3

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim userMsg As String

userMsg = Microsoft.VisualBasic.InputBox("What is your message?", "Message Entry Form", "Enter your messge here ", 100, 200)

If userMsg <> "" Then MessageBox.Show(userMsg) Else MessageBox.Show("No Message") End If End Sub End Class

The inputbox will appear as shown in the figure below when you press the

command button

Figure 12.2

7. The Built-In Functions

There are many built-in functions In Visual Basic 2012. In this lesson,

you will learn a couple of built-in functions that deal with string

manipulation.

13.1 The Mid Function

The Mid function is used to retrieve a part of the text from a given phrase.

The syntax of the Mid Function is

Mid(phrase, position,n)

*phrase is the string from which a part of the text is to be retrieved

*position is the starting position of the phrase from which the retrieving

process begins.

*n is the number of characters to retrieve.

Example 13.1

Public Class Form1 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim myPhrase As String myPhrase = Microsoft.VisualBasic.InputBox("Enter your phrase") Label1.Text = Mid(myPhrase, 2, 6) End Sub End Class

* This program will extract text starting from position 2 of the phrase and

the number of characters extracted is 6.

The figures are shown below:

Figure 13.1

Figure 13.2

13.2 The Right Function

The Right function extracts the right portion of a phrase. The format is

Microsoft.Visualbasic.Right ("Phrase", n)

Where n is the starting position from the right of the phase where the

portion of the phrase is going to be extracted. For example:

Microsoft.Visualbasic.Right ("Visual Basic", 4) = asic

Example 13.2

The following code extracts the right portion any phrase entered by the

user.

Private Sub Button1_Click (ByVal sender As System.Object, ByVal e As

System.EventArgs) Handles Button1.Click

Dim myword As String

myword = TextBox1.Text

Label1.Text = Microsoft.VisualBasic.Right (myword, 4)

End Sub

13.3 The Left Function

The Left function extracts the left portion of a phrase. The format is

Microsoft.Visualbasic.Right ("Phrase", n)

Where n is the starting position from the left of the phase where the portion

of the phrase is going to be extracted. For example:

Microsoft.Visualbasic.Left("Visual Basic", 4) = asic

Example 13

The following code extracts the left portion any phrase entered by the user.

Private Sub Button1_Click (ByVal sender As System.Object, ByVal e As


Dim myword As String

myword = TextBox1.Text

Label1.Text = Microsoft.VisualBasic.Left (myword, 4)

End Sub

13.4 The Trim Function

The Trim function trims the empty spaces on both sides of the phrase. The

format isTrim("Phrase").For example,

Trim (” Visual Basic “) = Visual basic

Example 13.4

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As


Dim myPhrase As String

myPhrase = Microsoft.VisualBasic.InputBox("Enter your phrase")

Label1.Text = Trim(myPhrase)

End Sub

13.5 The Ltrim Function

The Ltrim function trims the empty spaces of the left portion of the phrase.

The format is Ltrim("Phrase").For example,

Ltrim (" Visual Basic 2012")= Visual basic 2012

13.6 The Rtrim Function

The Rtrim function trims the empty spaces of the right portion of the

phrase. The format is Rtrim("Phrase"). For example,

Rtrim ("Visual Basic 2012 ") = Visual Basic 2012

13.7 The InStr function

The InStr function looks for a phrase that is embedded within the original

phrase and returns the starting position of the embedded phrase. The format

is

Instr (n, original phase, embedded phrase)

Where n is the position where the Instr function will begin to look for the

embedded phrase. For example

Instr(1, "Visual Basic 2012 ","Basic")=8

*The function returns a numeric value.

You can write a program code as shown below:



Label1.Text = InStr(1, "Visual Basic", "Basic")

End Sub

13.8 The Ucase and the Lcase Functions

The Ucase function converts all the characters of a string to capital letters.

On the other hand, the Lcase function converts all the characters of a string

to small letters.

The syntax is

Microsoft.VisualBasic.UCase(Phrase)

Microsoft.VisualBasic.LCase(Phrase)

For example,

Microsoft.VisualBasic.Ucase("Visual Basic") =VISUAL BASIC

Microsoft.VisualBasic.Lcase("Visual Basic") =visual basic

13.9 The Chr and the Asc functions

The Chr function returns the string that corresponds to an ASCII code

while the Asc function converts an ASCII character or symbol to the

corresponding ASCII code. ASCII stands for “American Standard Code

for Information Interchange”. Altogether there are 255 ASCII codes and as

many ASCII characters. Some of the characters may not be displayed as

they may represent some actions such as the pressing of a key or produce

a beep sound. The format of the Chr function is

Chr(charcode)

and the format of the Asc function is

Asc(Character)

The following are some examples:

Chr(65)=A, Chr(122)=z, Chr(37)=% ,

Asc("B")=66, Asc("&")=38

8. The Math Functions

In this lesson, you will learn how to use the built-in math functions in

Visual Basic 2012. There are numerous built-in math functions in Visual

Basic 2012. Let’s examine them one by one.

14.1 The Abs function

The Abs function returns the absolute value of a given number.

The syntax is

Math. Abs (number)

* The Math keyword indicates that the Abs function belong to the Math

class.

14.2 The Exp function

The Exp of a number x is the exponential value of x, i.e. ex . For example,

Exp(1)=e=2.71828182

The syntax is

Math.Exp (number)

Example 14.1



Dim num1, num2 As Single

num1 = TextBox1.Text

num2 = Math.Exp(num1)

Label1.Text = num2

End Sub

14.3 The Fix Function

The Fix function truncates the decimal part of a positive number and

returns the largest integer smaller than the number. However, when the

number is negative, it will return smallest integer larger than the number.

For example, Fix(9.2)=9 but Fix(-9.4)=-9

Example 14.2





num2 = Fix(num1)

Label1.Text = num2

End Sub

14.4 The Int Function

The Int is a function that converts a number into an integer by truncating

its decimal part and the resulting integer is the largest integer that is smaller

than the number. For example

Int(2.4)=2, Int(6.9)=6 , Int(-5.7)=-6, Int(-99.8)=-100

14.5 The Log Function

The Log function is the function that returns the natural logarithm of a

number. For example, Log(10)=2.302585

Example 14.3





num2 = Math.Log(num1)

Label1.Text = num2

End Sub

* The logarithm of num1 will be displayed on label1

14.6 The Rnd( ) Function

Rnd is a very useful function in Visual Basic 2012 . We use the Rnd

function to write code that involves chance and probability. The Rnd

function returns a random value between 0 and 1. Random numbers in their

original form are not very useful in programming until we convert them to

integers. For example, if we need to obtain a random output of 6 integers

ranging from 1 to 6, which makes the program behave like a virtual dice,

we need to convert the random numbers to integers using the formula

Int(Rnd*6)+1.

Example 14.4



Dim num as integer

Num=Int(Rnd()*6)+1

Label1.Text=Num

End Sub

In this example, Int(Rnd*6) will generate a random integer between 0 and

5 because the function Int truncates the decimal part of the random number

and returns an integer. After adding 1, you will get a random number

between 1 and 6 every time you click the command button. For example,

let say the random number generated is 0.98, after multiplying it by 6, it

becomes 5.88, and using the integer function Int(5.88) will convert the

number to 5; and after adding 1 you will get 6.

14.7 The Round Function

The Round function is a Visual Basic 2012 function that rounds up a

number to a certain number of decimal places. The Format is Round (n, m)

which means to round a number n to m decimal places. For example,

Math.Round (7.2567, 2) =7.26

Example 14.5





num2 = Math.Round(num1, 2)

Label1.Text = num2

End Sub

* The Math keyword here indicates that the Round function belong to the

Math class.

9. The Format Function

The Format function in Visual Basic 2012 is to display the numbers in

different formats. There are two types of Format functions, one of them is

the built-in format function and the other one is defined by the users.

(i) The syntax of the predefined Format function is

Format (n, "style argument")

where n is a number.

The list of style arguments in Visual Basic 2012 is given in Table 15.1.

Table 15.1 List of style arguments

Style

argument Explanation Example

General

Number

To display the number without

having separators between

thousands.

Format(8972.234,

“General

Number”)=8972.234

Fixed

To display the number without

having separators between

thousands and rounds it up to two

decimal places.

Format(8972.2,

“Fixed”)=8972.23

Standard

To display the number with

separators or separators between

Format(6648972.265,

“Standard”)=

6,648,972.27

thousands and rounds it up to two

decimal places.

Currency

To display the number with the

dollar sign in front has separators

between thousands as well as

rounding it up to two decimal

places.

Format(6648972.265,

“Currency”)=

$6,648,972.27

Percent

Converts the number to the

percentage form and displays a %

sign and rounds it up to two

decimal places.

Format(0.56324,

“Percent”)=56.32 %

Example 15.1


System.EventArgs) Handles Button1.Click, Button5.Click, Button4.Click,

Button3.Click

Label1.Text = Format(8972.234, "General Number")

Label2.Text = Format(8972.2, "Fixed")

Label3.Text = Format(6648972.265, "Standard")

Label4.Text = Format(6648972.265, "Currency")

Label5.Text = Format(0.56324, "Percent")

End Sub

The Output window is shown below:

Figure 15.1

(ii) The syntax of the user-defined Format function is

Format (n, "user's format")

Although it is known as user-defined format, we still need to follow certain

formatting styles. Examples of user-defined formatting style are listed in

Table 15.2

Table 15.2 User-Defined format

Example 15.2


System.EventArgs) Handles Button1.Click, Button5.Click, Button4.Click,

Button3.Click

Label1.Text = Format(8972.234, "0.0")

Label2.Text = Format(8972.2345, "0.00")

Label3.Text = Format(6648972.265, "#,##0.00")

Label4.Text = Format(6648972.265, "$#,##0.00")

Label5.Text = Format(0.56324, "0%")

End Sub

The Output window is shown below:

Figure 15.2

10. Formatting Date and Time

16.1 Formatting Date and time using predefined formats

In Visual Basic 2012, we can format date and time using predefined

formats or user-defined formats. The predefined formats of date and time

are shown in Table 16.1.

* Instead of “General date”, you can also use the abbreviated format “G”,

i.e. Format (Now, “G”). For “Long Time”, you can use the abbreviated

format “T” and for “Short Time”, you may use the abbreviated format “t”

https://www.vbtutor.net/wordpress/wp-content/uploads/2012/04/vb2010_table16.11.jpg

Example 16.1



Label1.Text = Format(Now, "General Date")

Label2.Text = Format(Now, "Long Date")

Label3.Text = Format(Now, "short Date")

Label4.Text = Format(Now, "Long Time")

Label5.Text = Format(Now, "Short Time")

End Sub

6.2 managing variables€¦ · label1.text = cstr(sum) label2.text = cstr(difference) label3.text =...

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